The present invention relates to a dielectric filter installed in a terminal of a radio communication system; and, more particularly, to a dielectric filter having a notch pattern, in which an attenuation characteristic on a stop band can be improved and simultaneously a coupling quantity control between respective resonators can become easy, by gaining a high attenuation pole even without increasing the number of resonators.
It is known that in order to improve frequency efficiency in the terminals of a radio communication system, mutually neighboring transmission and reception frequency bands may be used, such that a high attenuation characteristic on a stop band is required in a filter used in such terminals.
Referring to FIGS. 1 through 3, a dielectric filter based on first through third embodiments of a conventional technique may be described as follows.
The dielectric filter based on the first embodiment of the conventional technique shown in FIG. 1 includes a dielectric block 10 and first through sixth resonators 11, 12, 13, 14, 15 and 16 which are formed, piercing through upper and lower faces of the dielectric block 10.
Each resonator 11 through 16 is formed by plating an inner wall face of a through-hole with conductive metal, the through-hole being formed by piercing through the upper and lower faces of the dielectric block 10. All the wall faces of the dielectric block 10 except the upper face are plated with the conductive metal. The upper face of the dielectric block 10 is electrically opened, and the rest of the wall faces, except the upper face, of the dielectric block 10 are formed as ground faces.
On the upper face of the dielectric block 10, a plurality of slots 17 for controlling a coupling quantity between two resonators formed adjacently to each other, and a reactance 18 for improving an attenuation characteristic on a stop band of the dielectric filter are formed. An inner wall face of each slot 17 is plated with conductive metal, and the coupling quantity between the resonators of the filter can be controlled by controlling a size of the slot 17. The reactance 18 connects two resonators, namely, a second resonator 12 with a fifth resonator 15, and resonators 13, 14 not connected by the reactance 18 exist between two resonators, namely, the second and fifth resonators 12, 15, which are connected by the reactance 18. This reactance 18 is composed of coil, a capacitor and a lead wire etc.
The dielectric filter based on the second embodiment of the conventional technique shown in FIG. 2 includes a dielectric block 20 having a formation of first through seventh resonators 21, 22, 23, 24, 25, 26 and 27 which are formed, piercing through upper and lower faces thereof.
A first transmission line 28 having an electric length of xcex/4 is formed between the first and second resonators 21, 22, xcex being a wavelength of resonance frequency. Also, a second transmission line 29 having an electric length of xcex/4 is formed between the second and third resonators 22, 23. Such a conventional dielectric filter has numerous attenuation pole characteristic through an inverter circuit. At this time, a magnetic field coupling is formed between the respective resonators, and such respective resonators are separately tuned so as to have a desired filter characteristic.
If the dielectric filter based on the second embodiment of the conventional technique is applied to a duplexer, a plurality of resonance polar points can be formed by forming numerous holes.
The dielectric filter based on the third embodiment of the conventional technique shown in FIG. 3 includes a dielectric block 30 in which an electric opening face is formed on an upper face thereof, and on its side wall and lower face, ground faces plated with the conductive metal are formed, and in which first through fourth resonators 31, 32, 33, 34 formed piercing through the upper and lower faces thereof are also provided.
On the upper face of the dielectric block 30 as the opening face, there are formed first through fourth resonator patterns 31a, 32a, 33a and 34a connected to upper parts of the respective resonators 31 through 34, and two of first metal patterns 35 provided between the second and third resonator patterns 32a, 33a and between the third and fourth resonator patterns 33a, 34a. Both end parts of the first metal pattern 35 are individually connected to both side wall faces as the ground face of the dielectric block 30. Further, a second metal pattern 36 is formed between the first and second resonator patterns 31a, 32a, and one end part of the second metal pattern 36 is connected to one side wall face of the dielectric block 30, and another end part provides an opening part 37 which is distanced by a constant interval T from another side wall face of the dielectric block 30.
In such conventional dielectric filter, a loading capacitance is formed between the respective metal patterns 35 and the second through fourth resonator patterns 32a to 34a, and a loading capacitance is also formed between the first and second resonator patterns 31a, 32a. Herewith, the loading capacitance between the first and second resonator patterns 31a, 32a is controlled by a size of the opening part 37 formed by the second metal pattern 36. In other words, the loading capacitance between the first and second resonator patterns 31a, 32a can be controlled by controlling a size of the opening part 37.
In the dielectric filter based on the first embodiment of the conventional technique, more than three resonators must be formed to improve the attenuation characteristic on the stop band by using the reactance, such that the size of the filter is increased and it is difficult to reduce or enlarge a size of a slot that has already been processed. Thus, it is difficult to control a coupling quantity between the resonators after a process of the filter.
Furthermore, in case that the dielectric filter based on the conventional second embodiment is applied to a duplexer, an impedance unbalance unacceptable in an interface of transmission/reception filters occurs from an attenuation pole formed on a pass band end portion of the transmission filter coupled with the reception filter. That is, the number of the attenuation poles is restricted as a transmission zero, to thereby drop a filter characteristic on the stop band, and due to such reasons, some restriction is caused in designing the transmission/reception filters of the duplexer.
In the dielectric filter based on the conventional third embodiment, the coupling quantity can be controlled by controlling a size of the opening part formed by the second metal pattern, but the number of the resonators must be increased to improve the attenuation characteristic on the stop band. Therefore, there is a problem in that the filter becomes large in size.
Therefore, it is an object of the present invention to provide a dielectric filter having a notch pattern capable of improving an attenuation characteristic on a stop band, without increasing the number of resonators, through an embodiment for gaining a coupling not only between neighboring resonators but also between resonators which are not adjacent to one another, so as to obtain a high attenuation pole on a frequency band adjacent to transmission and reception frequency.
Another object of the present invention is to provide a dielectric filter having a notch pattern capable of easily controlling a coupling between a ground face and a resonator necessary for an operation of a filter and a coupling between a resonator and a resonator.
Still another object of the present invention is to provide a dielectric filter having a notch pattern capable of miniaturizing a filter without increasing the number of resonators.
In accordance with the present invention for achieving the above objects, the dielectric filter having a notch pattern includes a dielectric block in which a ground face plated with conductive metal for all the portions of the block except an upper face thereof and two side portions of one side wall face connected to the upper face is formed, and a plurality of resonator patterns and a plurality of metal patterns plated with the conductive metal are formed on the non-conductive upper face, with the resonator patterns being separated from the metal patterns by predetermined distances. An input electrode is provided on one of the non-conductive side portions and formed so that a signal from the outside may be inputted thereto, and at least two resonators are formed piercing through upper and lower faces of the dielectric block, a lower end part of such resonators being short-circuited with a lower face as the ground face of the dielectric block. Two resonators are connected with each other through a pattern formed on the upper face of the dielectric block in order to resonate and wave-transfer a signal inputted through the input electrode, and an output electrode is provided in the remaining non-conductive side portion on one side wall face of the dielectric block, the output electrode being for outputting a signal resonated in each resonator to the outside.